The technique of percutaneous transluminal coronary angioplasty (PCTA), wherein a preshaped or flexible guiding catheter is introduced into a cardiovascular system through the femoral or brachial artery under local anesthesia, is known in art. The guiding catheter is positioned in the entrance of the target coronary artery. A dilatation catheter with an expandable balloon tip is advanced through the guide catheter and manipulated into the branches of the coronary artery until the balloon is appropriately centered on the stenotic target lesion. The balloon is then inflated with a radiopaque contrast, which is a liquid that enables one to locate the position of the catheter using X-rays. The balloon applies pressure in a direction generally radial to the vessel wall to compress and remold the atherosclerotic material into a significantly more patent internal configuration. Current balloon dilatation catheters employ a fixed or movable steerable guide wire which negotiates the serpentine coronary vasculature in an atraumatic fashion to provide a path for the passage of the dilatation catheter.
Inflation of conventional dilatation balloons completely blocks the artery, and thus interrupts distal coronary blood flow. The duration of balloon inflation is of necessity limited by the resulting coronary ischemia, and manifest or incipient clinical instability. Typical inflation times may range from 15 seconds to 120 seconds. Maintenance of coronary perfusion during dilatation would greatly enhance the safety of coronary angioplasty, particularly in vessels serving large areas of myocardium. Prolonged inflation times would also be desirable to increase the likelihood of adequate vessel patency post-dilatation. Prolonged balloon inflation times also increase the probability of maintaining vessel patency or opening, following abrupt arterial closure due to intimal disruption, vessel dissection, or endoluminal thrombus formation.
In addition, it is known that the process of angioplasty injures the inner surfaces of the involved artery. It is believed that a condition known as restenosis is to some degree initiated by this injury to the artery. Restenosis is the recurrence of severe renarrowing in a coronary artery at the site of prior angioplasty, and to some degree, the condition of restenosis involves the growth and proliferation of scar tissue initiated by angioplasty. Thus, there is a need for balloon designs resulting in a lesser degree of vessel wall injury than that caused by current balloon designs. Current balloon designs have more surface area in contact with the vessel wall and are therefore more likely to cause extensive disruption to the cellular lining of the vessel.
Therefore, it would be desirable for an angioplasty catheter to provide for continuous blood flow (perfusion) past the stenotic region in the target coronary vessel even during periods of balloon inflation, and to provide for a lesser degree of vessel wall injury upon inflation. Such a perfusion dilatation catheter would permit prolonged balloon inflations to achieve the advantages elaborated above without provoking clinical instability, as long as the inflated balloon catheter assembly provides physiologically adequate coronary flow rates. However, in order for a perfusion angioplasty catheter to be of true clinical utility and suitable for routine use as the dilatation catheter of first choice by medical practitioners of the art, it must additionally incorporate advances available in the current genre of angioplasty catheters. Some of these advances include: balloons having a small diameter when collapsed, so as to enable the balloon to pass through abnormal areas of extreme constriction or blockage; balloons having excellent tracking ability over steerable coronary guide wires, such that the balloons conform to the paths of the guide wires; and balloons having enhanced pushability through tortuous coronary circulation and through severely stenotic lesions.
Numerous angioplasty catheters which afford varying degrees of coronary perfusion during balloon inflation have been described in the prior art. However, none of these catheters incorporate all of the necessary attributes mentioned above into a single device, and hence these catheters are not suitable for widespread first line use.
U.S. Pat. No. 4,790,315, to Mueller, Jr. et al. discloses a perfusion catheter wherein small holes are placed in the hollow shaft of the catheter adjacent to the proximal and distal ends of the balloon. These holes provide a flow path for blood during the angioplasty process and if the vessel collapses following dilatation. The cross-sectional area provided for flow, however, is small and suboptimal.
U.S. Pat. No. 4,877,031 to Conway et al. discloses a steerable perfusion dilatation catheter with a fixed guide wire assembly. The steerable guide wire in this device is integral to the dilatation catheter and does not have to be removed to optimize coronary flow during balloon inflation. This device, however, again provides limited cross-sectional area for coronary blood flow and exhibits an increased collapsed crossing profile which limits its ability to traverse lesions of critical stenotic severity. Any increase in the cross-sectional area of the hollow central balloon catheter shaft to augment perfusion rates further increases the crossing profile and also decreases its desirable flexibility and tracking properties.
U.S. Pat. No. 4,581,017 to Sahota also discloses a perfusion balloon wherein flow is achieved during balloon inflation through the hollow central shaft of the catheter by means of proximal and distal shaft side holes. In addition, Sahota discloses angioplasty catheters of complex construction which incorporate multiple small balloons deployed circumferentially around a central hollow shaft and which further incorporate multiple individual tubular ports for inflation and deflation of the balloon subunits. Some designs use a single dilating balloon in which significantly thickened portions of the balloon wall are provided for non-uniform compliance during inflation. The complex construction of the balloons of Sahota severely decreases their flexibility, trackability, and markedly increases their lesion crossing profile. These limitations have continued to prevent adaptation of balloons of said design to clinical art.
Similar limitations apply to the steerable perfusion angioplasty dilatation catheter disclosed in U.S. Pat. No. 4,892,519 to Songer et al. The device of Songer et al. also has an integral but movable guide wire which cannot be removed or replaced if the technical complexities of the procedure require it.
U.S Pat. No. 4,909,252 to Goldberger discloses a perfusion angioplasty balloon having a donut-shaped cross-section with a central opening which provides for blood flow through a passage, when the balloon is inflated. This device, however, utilizes a complex balloon geometry requiring redundant balloon surface folds which greatly enlarge the collapsed crossing profile of the angioplasty balloon and also limit the flexibility and tracking of the distal balloon assembly.
U.S. Pat. Nos. 4,601,713, 4,710,181, and 4,738,666, all to Fuqua, and European Patent No. 400,713 to Deuss, disclose balloon catheters wherein an expandable balloon tip capable of exhibiting several discrete diameters is achieved. The balloon material folds on itself redundantly in the longitudinal dimension to provide one or more invaginations which are constrained either by an external retaining sheath or by heat welds of limited strength. The balloon catheter achieves a second and larger diameter when the constraints are physically removed or are overcome by sufficient inflation pressure. The folds of these longitudinal invaginations, however, are in contiguity and do not afford blood flow during balloon inflation.
It is apparent that what has been needed and heretofore unavailable are perfusion angioplasty balloon catheters which provide excellent and physiologically adequate coronary blood flow past the area of lesion stenosis without compromising or limiting other necessary and desirable properties of the angioplasty catheter assembly. These attributes, as outlined above, include the low lesion crossing profile, fully exchangeable guide wire capability, and favorable tracking, flexibility, and longitudinal force transmission characteristics provided by the current genre of non-perfusion angioplasty balloon catheters. The present invention satisfies these needs.